Humans are constantly exposed to the vast mixture of chemicals that are present in our environment. Often this mixture (e.g urban air) contains both carcinogenic polycyclic aromatic hydrocarbons and other types of polycyclic hydrocarbons that can act both as cocarcinogens with some carcinogenic hydrocarbons and as inhibitors of carcinogenesis with others. In addition, mixtures such as cigarette smoke contain other classes of chemicals which can alter the effects of exposure to carcinogenic polycyclic hydrocarbons by acting as cocarcinogens or as tumor promoters. To determine the mechanism by which certain hydrocarbons can potentiate the carcinogenicity of some carcinogenic hydrocarbons and inhibit cancer induction by others, their effects on the metabolic activation of carcinogenic polycyclic aromatic hydrocarbons and the induction of biological effects will be measured in hamster embryo cell cultures. These studies will include quantitative measurements of hydrocarbon oxidation, conjugation, DNA-interaction products and the induction of cytotoxicity, cell-mediated mutation and transformation. The role of conjugation of hydrocarbon metabolites to glucuronic acid in the induction of bioligical effects will be examined. The effects of other types of modifiers such as cocarcinogens of other classes and tumor promoters on the above parameters will also be measured. The results obtained will be of use in predicting how the effects of exposure to carcinogens are altered in the presence of hydrocarbons and other types of cocarcinogens and tumor promoters. This will permit modification of these effects and aid in the development of short term assays with enhanced sensitivity for the detection of carcinogens in the environment.